Blood vessel cannulation technique is used for long-term sampling or multiple sampling over a relatively short time period.
Catheters reduce the stress and discomfort associated with multiple sampling techniques such as repeated restraint and needle stick. In addition to blood sampling, catheterization should be considered for repeated substance administration or continuous ambulatory infusion.

Before beginning any blood sampling protocol, careful consideration should be given to matching the best possible technique to your experimental goals. The choice of technique will depend on a range of factors, including:

• The purpose of the blood collection, e.g. biochemical analysis, DNA extraction etc.
• The need for an arterial versus venous sample.
• The duration and frequency of sampling.
• The health status of the animal being bled.
• Whether the sample is taken as a repeat or terminal procedure.
• The potential for stress-induced effects on biochemical and hematological parameters.